1. Field of the Invention
The present invention relates to a parallel mechanism, and in particular, to a parallel mechanism including a pair of arms coupled together through a ball joint.
2. Description of Related Art
A parallel mechanism in which a base portion that includes a support base and a bracket with an end effector attached thereto are coupled together in parallel through a plurality of arms is known. That is, in the parallel mechanism, electric motors are arranged in parallel. Furthermore, a plurality of arms coupled to the respective motors ultimately operate one bracket.
In each arm, a ball and a socket provided in a ball joint are held by the tensile force of a spring. However, one half side of the ball of the ball joint is exposed from the socket. Thus, when the ball joint is subjected to a load exceeding the tensile force of the spring, the ball may come loose from the socket. However, conventional techniques for arranging the parallel mechanism do not take into account sensing of possible loosening of the ball joint. Thus, even if the ball joint comes loose, the parallel mechanism continues to operate with no measures taken, that is, it continues to operate with the ball joint remaining loose. When the parallel mechanism continues to operate with the ball joint remaining loose, the arm or the like may be damaged. Thus, there has been an unmet demand to sense when the ball joint, through which the arms or the like are swingably coupled together, is loose.